In his new book, biologist Rob Dunn describes the relationships our bodies have with the organisms that share our world— from the effects of antibiotic soap on skin, to theories about why some people develop Crohn's disease, to new thinking about the role of appendixes.

IRA FLATOW, Host:

You're listening to SCIENCE FRIDAY. I'm Ira Flatow. Are you one of those hand sanitizer junkies? You know, the type you can't go anywhere in public without that little bottle of clear alcohol gel? You touch your shopping cart, you hang on to a subway pole, you turn a doorknob, better decontaminate and fast.

P: Predators, Parasites, and Partners That Shape Who We Are." He write about how natural it is for our bodies to be covered with microbes.

We did, after all, evolve in a world crawling with creatures. You've got your bacteria, parasites and worms. Could they be serving some purpose - a useful purpose - in our bodies? Joining me now is Rob Dunn, associate professor in the Department of Biology at North Carolina State University in Raleigh. Welcome to SCIENCE FRIDAY.

ROB DUNN: Thanks so much, Ira, it's great to be here. What a great heart show. I really enjoyed it.

FLATOW: Thank you. Let's talk about your book. Your book is more than just about the bacteria that live on us, right? It's really about how we evolved with creatures around us. I mentioned the worms, but you have cows, predators and things like that.

DUNN: Yes, I'm a community ecologist by training. So I study how organisms interact with each other. And I've become really interested in humans and all of the other species we interact with and how they've changed through time and what that means for how we are and really who we are in some really fundamental sorts of ways.

FLATOW: And so, is it a mistake to use that hand washer, those alcohol gels?

DUNN: So it is. I mean, so the alcohol gels are okay. They don't appear to do a whole lot, but they're not necessarily bad. But a lot of what we use is actually antimicrobial or antibacterial and it has triclosan in it, and there have been a couple of really good studies, recently, comparing households who use just normal soap to those that use the soap with triclosan in it.

And it turns out that about 75 percent of us use at least some antimicrobial substance in our house, whether it's a wipe or a soap, or - it's actually really common in detergents.

And when you compare, head-to-head, those households, the households that use just normal soap are about the same, in terms of health, as the households who use the antibacterial or antibiotic soap.

And for those individuals in one recent study who were chronically diseased before the study, so they had asthma or diabetes - I mean, very, very common chronic diseases - when they used the antibiotic soaps, they were actually more likely to get sick than if they didn't use any soap at all.

And so there's something really fundamental that these soaps are potentially doing to us, and it relates to the good life we have on our skin.

FLATOW: So there is good stuff that we're killing with these antimicrobial soaps and gels?

DUNN: Yeah. So what we think that normal soap does is that when you're washing your hands, is that it tends to kill what's recently arrived. And so if you just shook the hand of somebody who had E. coli on their hand, or you just touched something, or, you know, you just wiped in the bathroom - it's scrubbing off those recent arrivals but largely leaving intact the many, many bacteria that would be on your hand normally, and that are providing a benefit, a kind of first line of defense.

It's not actually well-documented that that's what's going on, but that's the sort of generally held belief of how soaps work. But when you're using these antibiotic soaps, they're having a slightly different effect. Because what they're doing is they're favoring a subset of species that are tough enough to deal with that antibiotic compound.

And there are actually some bacteria that now appear to eat the antibiotic compound in those soaps and wipes - if they have carbon, which is pretty easy to get, pretty much anywhere you are. And so the antibacterial soap's really pretty fundamentally different, and we use them all the time without thinking much about what they're doing.

FLATOW: 1-800-989-8255 is our number. We're talking with Rob Dunn, author of "The Wildlife," or "The Wild Life," whichever way you'd like to pronounce it. It's two words in your book. "The Wild Life Of Our Bodies: Predators, Parasites, and Partners That Shape Who We Are Today." Our number, 1-800-989-8255. You can tweet us @scifri, @-S-C-I-F-R-I, or go to our Facebook /scifri on Facebook.

There's so much to talk about in your book. Let's move on to Crohn's disease. It can be a debilitating disease. It's very common in developed countries, and you talk about some unusual methods to treat it that we might not think about.

DUNN: Yeah, so there's more and more evidence of a geographical association between the places where people get Crohn's disease and where we've removed worms from our systems. And so historically, most humans would have multiple species of worms...

FLATOW: Do you mean like fishing worms or different kinds of worms that we see in our guts.

DUNN: No, whipworms, tapeworms, hookworms, roundworms. It was a zoo in our guts. And very recently, really in the last 50 years in most places, we've started to pretty comprehensively rid ourselves of worms in some places but not all parts of the world.

And so it's in those places that autoimmune disease like Crohn's disease have started to become more common (technical difficulties). A number of people have begun to argue that maybe these are causally associated.

And so one of the first things that was done was a guy by the name of Joel Wienstock at Tufts did an experiment where he actually gave Crohn's patients whipworms and was able to show that the patients given whipworms that had Crohn's actually saw remission in most of the symptoms of Crohn's.

And so there's one interesting piece of evidence that maybe there is some relationship between the worms and Crohn's. And then there are other studies coming up. There are some really good studies in mice and in a study in Gabon in West Africa showing that if children have a whole bunch of worms, which is really common, and then you get rid of those worms, and then you have a control group in which you don't get rid of the worms, the children that you've ridded of the worms are then much likely to have allergies.

And so there's this growing sense of this link between the presence of worms and what our immune system is doing and the sort of broad sense that in the absence of worms, our immune system can be kind of over-reactive.

FLATOW: Wow, so are there any studies to test out this theory that if you have people with Crohn's syndrome, let's give them some worms and see how they improve?

DUNN: Yeah, so there's a good study, folks in Iowa, and those individuals that were given worms in Gatorade, worm eggs in Gatorade, actually got much better. All but one individual in that case who had Crohn's got better.

And there are now a couple of groups in Mexico that are clinically giving people with Crohn's worms. And so you can go to Mexico if you have Crohn's and get a worm treatment.

But I think one of the interesting things related to this is like lots of what's going on between our body and other species, it's still really a brave new world. And so we understand these relationships that take the worms away and some bad things seem to happen, put them back, and you seem to restore some benefits.

But exactly what's going on is wide open, and so for me personally, if somebody's interested in these interactions between species, it's really amazing that something so fundamental to who we are and so intimate could still be so poorly understood.

BOB: Hi, well, let me just make this quick. I work in the health field, and we - I've always heard stories, folk lore about that Crohn's. So to hear it actually stated by an author is great. But - and that was my question, do it. But I have another question, and it's real quick.

When I was growing up, you know, back in the '60s, you know, there used to be like open sewers and stuff. And we used to - as kids, we used to love to explore the sewer system, you know, going in sewer tunnels where there was open sewage.

Now, I think back, you know, we walked in our shoes, and then we'd go in the house with the shoes. And I was thinking, you know - and I also read this when I was being educated in the health field about the Western societies having - we have so much autoimmune diseases because at a young age, we're not exposed to bacteria. We don't give our systems like - you know, we don't allow them to build, like a muscle.

And I was wondering what do you think about that? Should kids be exposed to, you know, instead of mothers washing vegetables and using all these antibacterial stuff, is it better for them to be exposed to germs and bacteria? And that's my question.

FLATOW: Good question. Thanks, Bob.

DUNN: Yes, so that's - I mean, it's a fascinating question, Bob. So, I mean, I think that on some level, there's a lot of evidence that kids are more exposed to more kinds of either good bacteria or sort of at least harmless bacteria do see some benefits.

And then the thing - the worm story is sort of separate in as much as most of the worms have some cost to us, but often it's not a huge cost. In the case of worms, I think ideally we'd either like to domesticate some of these worms so they have no cost and use them or identify the chemical compound.

FLATOW: Let's go to Laurie(ph) in Dublin, California. Hi, Laurie.

LAURIE: Hello, how are you?

FLATOW: How are you?

LAURIE: Great, thanks. I just want to say I've been a wastewater professional, aka a sewage treatment plant operator, for many, many years. I never use antibacterial soaps. I use regular bar soaps, even at work. I keep my nails short. I just use good hand-washing techniques. I don't use antibacterials at home, and everything that the author is saying substantiates what I know. I mean, of all people, you'd think that I would use antibacterials, but I'm not for them at all.

FLATOW: There you go. There's a testimonial for soap.

DUNN: Yeah. Thanks, Lori. I mean, soap is this miraculous thing. So, I mean, if you compare populations that use and don't use soap, using soap can reduce, you know, really common colds and flus and bacterial infections by 20 to 40 percent. And so it's a big deal, and it's so simple. And we seemed so eager to be hygienic, but the truth is about 50 percent of people don't regularly wash their hands with soap. And so rather than using all this antibacterial stuff, just wash your hands. People usually...

FLATOW: Hey, there you go. Tell us about your bellybutton biodiversity project. Wow.

DUNN: Yeah. So we've been fascinated by trying to figure out what's living on us, and this project really started just very small, but it's kind of caught on. And what we want to do - a lot of the time when we study the microbes in our body, we do it in a real intensive way. We pick five people, and we study them very much in depth. But we don't have a good sense, like if you look geographically or among populations, how people vary in the species that live on them. And so we started sampling people from all over and sampling their bellybuttons.

We just take a swab, swab their bellybutton and then, we grow the microbes from the bellybutton out on agar. But the truth is that most of the species that you find in your bellybutton, Ira, or anybody else finds, we don't know what they eat. And so the only way we can see those is by looking at them genetically. And so in doing that, I mean, just in the first 90 people we've looked at in terms of which species are present, we've found 1,400 species of bacteria, 600 of which don't match up with species we know so far.

And so it's like the rainforest in there. It's really this incredible thing. And I love it because when somebody knows what species live on them, they have to think about that life in a really different way. I mean, I found out that I have this rare species in my bellybutton. It's only known from soybeans and silk moths and meat. And it's sort inescapable now. Now, I have to think. Well, what do I do about this? What is it doing? Which I think as a society is really a good place to go.

FLATOW: So can anybody get their bellybutton swabbed or become part of the study if they want?

DUNN: Yeah. So if you go to our website at yourwildlife.org, you can then click on the bellybutton site and see how to get involved. And, you know, we're really excited to learn about your navel.

(SOUNDBITE OF LAUGHTER)

FLATOW: Oh, so many things I could say. I'm talking with Rob Dunn, author of "The Wildlife Of Our Bodies: Predators, Parasites and Partners That Shape Who We Are Today" on SCIENCE FRIDAY from NPR. 1-800-989-8255. If that's just in our bellybuttons, then there must be colonies all over our bodies and other places.

DUNN: Yeah. So, I mean, the truth is that no single individual human has ever been sampled comprehensively for all the microbes on their body. It's never been done. I'm actually out - right now, I'm doing a show for the Discovery Channel about microbes from dirty jobs, and we're going to try to see...

FLATOW: Oh, yeah.

DUNN: ...it comprehensively...

(SOUNDBITE OF LAUGHTER)

DUNN: ...what they have.

(SOUNDBITE OF LAUGHTER)

DUNN: But all the evidence points to there being thousands of species of bacteria on the average human body.

FLATOW: So we can decode the human genome, but we don't know what's growing on your skin, basically?

DUNN: No. That's right. And more of your genetic diversity. So if you just - so if we sequenced you, Ira, and all of the genes on you...

FLATOW: I'm going to volunteer for that sequence.

DUNN: Excellent.

(SOUNDBITE OF LAUGHTER)

DUNN: So, far more of the genes on you are microbial or fungal or viral than are human. And on the one hand, you think, well, why does that matter? But the truth is that also includes genes for doing things that are ecologically important, as it were. And so, for example, in your gut, helping you to digest things, producing, you know, useful vitamins, defending your skin. And so those genes are really coding for useful things. And so you think of yourself, we all think of ourselves as human, but the truth is we're this interesting symbiosis in which we've really ignored most of the partners.

FLATOW: Yeah. And what these - do these - do we pass these from one to another, do you think? Or do we just pick them off of surfaces?

DUNN: So for sure - I mean, so, contagious diseases would be one example of things we know we pass. And then, there are things like H. pylori, which we also know ways in which it's passed, which can cause ulcers in your gut. But in terms of the good bacteria, we understand much less about them, and I think part of the issue is that when we look at our own bodies we tend to approach them from a medical perspective. So when they're broke, we say how do we fix them, how do we repair the heart? But I think when it comes to these other species, we also need to approach them from an ecological evolutionary perspective, how did they get the way they are, and what that that means about the ways they're likely to break?

FLATOW: One last question. Before we run out of time, I want to get this in here because in your book you talked about our appendix. And we all think that our appendix is useless, but we should rethink that?

DUNN: Yeah. I mean, the appendix amazes me because we've all thought it's useless, and it just hangs there. It's an organ. We seem comfortable with the idea we have a useless organ. But Bill Parker and Randall Bollinger at Duke have started to look into this, and a long story much shorter, it's now looking increasingly like the main role of the appendix is actually as kind of a nature reserve for our good bacteria. It's, in fact, filled with films of the bacteria that benefit us in our guts.

And it's also filled with a really common antibody in our gut, the most common one, IgA, and one of the main things IgA now does - has always done but it's been recently figured out that it does is that it helps those bacteria to form the links between themselves to keep from washing away. And so the amazing thing, I think, is our conscious brain is saying kill the bacteria and our subconscious immune system is saying hold onto them, keep them. But, so the idea that Parker and Bollinger have is that when you get some severe infectious disease in your gut and your intestines that might wipe out your native bacteria, that the appendix then serves as a place to - from which to recolonize your gut.

And much in the way that if you clear a forest and turn it to agriculture, well, where do the new seeds come from? Well, they come from the nature reserve next to the agricultural site. And so that's what they think the appendix is, this sort of climax forest of our bodies. And they could still be wrong. But there are no papers criticizing their ideas, and their ideas are at least plausible, given what the observations are. And so I think it's just really fascinating that you and I could have - we could all have an organ that people are just beginning to understand.

FLATOW: Yeah. Rethinking it. Well, Rob, thank you for taking time to join us. Your book is fascinating - "The Wildlife Of Our Bodies: Predators, Parasites and Partners That Shape Who We Are Today." Thanks again. And have a good weekend.

DUNN: Oh, thanks so much, Ira, to you and your microbes.

(SOUNDBITE OF LAUGHTER)

FLATOW: Me, too. I'll thank them for you.

DUNN: All right.

(SOUNDBITE OF LAUGHTER)

FLATOW: We're going to take a short break. And when we come back, we're going to talk about, oh, bananas. Bananas, yes, we do have bananas but for how long? Stay with us. We'll find out more.

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